The need for effective and economical preservative compositions is well known. Many products require preservatives to protect against contamination and growth of microbes, including personal care products such as shampoos, creams, lotions, cosmetics, and soaps, household products such as laundry detergents, hard surface cleaners, fabric softeners, and various industrial products. In particular, personal care product compositions are a nutrient-rich media which benefit from the incorporation of preservatives to control the growth of microorganisms and to prevent spoilage. Generally, the shelf life of these products depends on the resistance to microbial spoilage of components contained therein. It is therefore desirable to formulate a preservative which controls microbial contamination in personal care products, household products, and industrial products.
For the foregoing applications the demand for stable broad-spectrum preservatives has increased. For example, formaldehyde and isothiazolone derivatives have been shown to be highly effective biocidal preservatives. U.S. Pat. No. 3,987,184 issued to Foelsch discloses 1,3-dimethylol-5,5-dimethylhydantoin (DMDMH) as a useful formaldehyde donor compound for the preservation of personal care products, cosmetics, and household and industrial products.
Research in formaldehyde donating compounds has been fruitful. For example, in the case of DMDMH, improved formulations and processing has resulted in compositions which contain very low amounts of free formaldehyde. (See U.S. Pat. No. 5,405,862.) In addition, governmental regulations currently demand low free formaldehyde products. Thus, it would be desirable to formulate a preservative system that contains minimal amounts of free formaldehyde.
Various compositions can be preserved using isothiazolones and DMDMH as a formaldehyde donor. Isothiazolone has never been pre-mixed with a formaldehyde donor in a stabilized mixture, such that the isothiazolone retains its activity as a preservative for any significant period of time, before adding these active components to an end-use product to be preserved. Instead, the actives are added separately to the composition to be preserved. It would be beneficial if a stable isothiazolone preservative system could be designed that contained a mixture of the actives, such that the addition to the end-product could be performed in a single step.
Isothiazolone is highly toxic and very unstable under most circumstances, such as when present in water or other reactive molecule. To make the compound stable large amounts of cationic salts are added and the isothiazolone is diluted (usually to about 14% or less). While under these conditions, isothiazolone is stable at room temperature at low pH (from 1-4). During storage and manufacturing conditions the temperature and pH may increase causing isothiazolone to become unstable. While highly useful for controlling bacteria, fungi and other contaminating microbes in end-use products, isothiazolone's instability under less than ideal conditions results in a marked loss of activity. Thus, it would be advantageous to provide a preservative system that contains isothiazolone which is stable at a broad range of temperature and pH.
Additionally, under very acidic pH conditions, some end-use products such as personal care products cannot be easily formulated with isothiazolone. At less acidic pH levels, comparatively greater amounts of isothiazolone are needed in a preservative formulation because there is some loss of activity. A preservative system should be easy to formulate and have low levels of stable isothiazolone, so that it is nontoxic and non-irritating, but still provides biocidal activity. Stable isothiazolone formulations which are effective at less acidic pH levels have not heretofore been easily obtained.
Furthermore, effective broad spectrum preservative systems that contain formaldehyde donors with low free-formaldehyde and stable isothiazolone for use in applications at less acidic pH levels, free of cationic salts and which are non-toxic are not readily available.